1. Field of the Invention
The present invention relates to a limit switch mechanism, and more particularly to a limit switch mechanism in which limit switches can be actuated by a cam mounted on a drive shaft.
2. Description of the Prior Art
FIGS. 1 and 2 of the accompanying drawings show a conventional limit switch mechanism as assembled in an electrically operated shutoff valve for controlling the flow of a fluid. The valve includes an output shaft 1 rotatable in opposite directions through about 90 degrees by a motor 2 through a planetary gear mechanism. A switch drive shaft 3 has on its right-hand end a sector gear 4 held in mesh with a gear 5 on the output shaft 1. The switch drive shaft 3 is thus rotatable in opposite directions through about 90 degrees in synchronism with the output shaft 1. The switch drive shaft 3 has a cam 6 fixed to its left-hand end. A switch arm 7 is shaped as shown in FIGS. 3(A), 3(B) and 3(C), and has a pair of arms 7a, 7b extending in confronting relation one on each side of the cam 6.
A pair of limit switches 8a, 8b are positioned so that their longitudinal axes extend normally to the axis of the switch drive shaft 3, the limit switches 8a, 8b being located outwardly of the arms 7a, 7b, respectively. The limit switches 8a, 8b are thus located laterally of each other. When the cam 6 is angularly moved in opposite directions, the arms 7a, 7b are displaced away from each other to actuate the limit switches 8a, 8b, respectively.
The limit switches 8a, 8b are positioned with respect to the switch drive shaft 3 as follows: The limit switches 8a, 8b project downwardly by a dimension h.sub.1 and upwardly by a dimension h.sub.2 beyond the switch drive shaft 3. The limit switches 8a, 8b have pushbuttons 8a-1, 8a-2, respectively, each spaced from the switch drive shaft 3 by a dimension w.sub.1. The prior limit switch mechanism is therefore disadvantageous in that the limit switches 8a, 8b take up a relatively large space around the switch drive shaft 3, and hence the mechanism is large in size and heavy in its entirety.